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United States Patent |
5,752,522
|
Murphy
|
May 19, 1998
|
Lesion diameter measurement catheter and method
Abstract
The invention provides methods and apparatus for determining
cross-sectional dimensions of body lumens, such as the diameter of a blood
vessel. According to one exemplary method, the diameter of a blood vessel
is measured by first inflating a balloon catheter within the lumen until
the balloon diameter matches the lumen diameter. Inflation may be at a
very low pressure and be constrained by the lumen, or may alternatively be
controlled by monitoring the flow within the lumen. The balloon includes
at least one measurement element which indicates the expanded balloon
cross-sectional area, circumference, or diameter. Optionally, the
measurement element provides a fluoroscopic, radiographic, or ultrasound
indication of the cross-sectional dimension. In alternative embodiments,
such dimensions may be transmitted to the distal end of the catheter, or
determined after deflation and removal of the catheter.
Inventors:
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Murphy; Richard (Mountain View, CA)
|
Assignee:
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Cardiovascular Concepts, Inc. (Portola Valley, CA)
|
Appl. No.:
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435288 |
Filed:
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May 4, 1995 |
Current U.S. Class: |
600/587; 600/505 |
Intern'l Class: |
A61B 005/103 |
Field of Search: |
128/774,748,780,673
604/97,99
606/191,192
|
References Cited
U.S. Patent Documents
4564014 | Jan., 1986 | Fogarty et al. | 128/334.
|
4651738 | Mar., 1987 | Demer et al. | 128/344.
|
4873989 | Oct., 1989 | Einzig | 128/692.
|
5045071 | Sep., 1991 | McCormick et al. | 604/280.
|
5135488 | Aug., 1992 | Foote et al. | 604/97.
|
5146922 | Sep., 1992 | Williamson et al. | 128/774.
|
5171299 | Dec., 1992 | Heitzmann et al. | 604/100.
|
5209730 | May., 1993 | Sullivan | 604/96.
|
5219355 | Jun., 1993 | Parodi et al. | 606/191.
|
5239982 | Aug., 1993 | Trauthen | 128/4.
|
5263928 | Nov., 1993 | Trauthen et al. | 604/53.
|
5275169 | Jan., 1994 | Afromowitz et al. | 128/673.
|
5316016 | May., 1994 | Adams et al. | 128/774.
|
5343874 | Sep., 1994 | Picha et al. | 128/774.
|
5364354 | Nov., 1994 | Walker et al. | 604/96.
|
5382261 | Jan., 1995 | Palmaz | 606/158.
|
5419324 | May., 1995 | Dillow | 128/653.
|
5431628 | Jul., 1995 | Millar | 604/100.
|
5465732 | Nov., 1995 | Abele | 128/772.
|
5484449 | Jan., 1996 | Amundson et al. | 606/108.
|
5499995 | Mar., 1996 | Teirstein | 606/192.
|
Foreign Patent Documents |
2 137 499 A | Oct., 1984 | GB.
| |
WO 95/14501 | Jun., 1995 | WO.
| |
WO 95/28885 | Nov., 1995 | WO.
| |
Other References
John E. Abele, "Balloon Catheters and Transluminal Dilation: Technical
Considerations," AJR 135:901-906, Nov. 1980.
Linda L. Demer et al., "High Intensity Ultrasound Increases Distensibility
of Calcific Atherosclerotic Arteries," J Am Coll Cardiol 18:1259-62, Nov.
1991.
Allen B. Nichols et al., "Quantification of Relative Coronary Arterial
Stenosis by Cinevideodensitometric Analysis of Coronary Arteriograms,"
Circulation 69:512-522, 1984.
Patrick W. Serruys et al., "Assessment of Percutaneous Transluminal
Coronary Angioplasty by Quantitative Coronary Angiography: Diameter Versus
Densitometric Area Measurements," Am J Cardiol 54:482-488, 1984.
Chuter, T. et al., "Anatomy of the Infrarenal Aortic Aneurysm," Endoluminal
Vascular Prostheses pp. 21-36; Little, Brown and Company; Boston (1995).
Chuter, T. et al., "Patient Selection and Preoperative Assessment,"
Endoluminal Vascular Prostheses pp. 255-283; Little, Brown and Company;
Boston (1995).
|
Primary Examiner: Buiz; Michael
Assistant Examiner: Rasche; Patrick W.
Attorney, Agent or Firm: Townsend and Townsend and Crew LLP
Claims
What is claimed is:
1. A method for measuring a cross-sectional dimension of a target location
of a body lumen, the method comprising;
inserting a catheter into the body lumen, wherein the catheter includes a
balloon;
aligning the balloon with the target location within the body lumen;
inflating the balloon within the body lumen so that a cross-section of the
balloon substantially matches the cross-section of the body lumen;
measuring a cross-sectional dimension of the balloon, wherein the
cross-sectional dimension of the balloon corresponds to a cross-sectional
dimension of the target location of the body lumen;
deflating the balloon, wherein the balloon does not suffer irreversible
changes during the inflating step; and
reusing the balloon.
2. A method as claimed in claim 1, further comprising sensing a flow
through the body lumen using a sensor coupled to the external surface of
the catheter.
3. A method as claimed in claim 1, wherein the inflating step comprises
introducing fluid into the balloon at a low pressure which is slightly
higher than the pressure within the lumen so as to fully expand a smaller
portion of the balloon which is smaller than the body lumen, but which
pressure does not fully expand a larger portion of the balloon which is
larger than the body lumen.
4. A method as claimed in claim 1, wherein the measuring step comprises
generating a signal indicating the cross-sectional dimension of the
inflated balloon with a cross-sectional dimension measurement element in
contact with the balloon, and transmitting the signal along a catheter
body.
5. A method as claimed in claim 4, wherein the measurement element varies
in at least one electrical characteristic with the cross-sectional
dimension, and the signal is transmitted electrically.
6. A method as claimed in claim 4, wherein the measurement element senses
the cross-sectional dimension mechanically, and the signal is transmitted
mechanically.
7. A method as claimed in claim 1, wherein the measuring step comprises
fluoroscopically or ultrasonically imaging at least one size indicating
element of the inflated balloon.
8. A method as claimed in claim 1 wherein the cross-sectional dimension of
the body lumen is a circumference.
9. A method as claimed in claim 1 wherein the cross-sectional dimension of
the body lumen is a diameter.
10. A method as claimed in claim 1 wherein the cross-sectional dimension of
the body lumen is a cross-sectional area.
11. A method for measuring a cross-sectional dimension of a target location
of a body lumen, the method comprising:
inserting a catheter into the body lumen, wherein the catheter includes a
balloon;
aligning the balloon with the target location within the body lumen;
sensing a flow through the body lumen using a sensor coupled to the
external surface of the catheter;
inflating the balloon within the body lumen so that a cross-section of the
balloon substantially matches the cross-section of the body lumen, wherein
the inflating of the balloon is halted when flow through the body lumen is
blocked; and
measuring a cross-sectional dimension of the balloon, wherein the
cross-sectional dimension of the balloon corresponds to a cross-sectional
dimension of the target location of the body lumen.
12. A method as claimed in claim 11, wherein the external sensor indicates
a physiological pressure within the body lumen acting on an outer surface
of the catheter.
13. A method as claimed in claim 12, wherein the measuring step comprises
measuring the difference between an internal balloon pressure and the
physiological pressure within the body lumen, the balloon being
elastomeric.
14. A method for measuring a cross-sectional dimension of a target location
of a body lumen having a flow, the method comprising:
inserting a catheter into the lumen, wherein the catheter includes a
balloon and a sensor in communication with an outside surface of the
catheter;
aligning the balloon with the target location within the body lumen;
inflating the balloon within the body lumen until the sensor indicates a
blockage of the flow; and
measuring a cross-sectional dimension of the inflated balloon while the
balloon is inflated within the body lumen, wherein the cross-sectional
dimension of the balloon corresponds to a cross-sectional dimension of the
target location of the body lumen.
15. A method as claimed in claim 14, further comprising over-expanding the
inflated balloon to an over-expanded cross-sectional dimension so that the
balloon distends the lumen wall, and recording at least one overexpanded
volume of an inflation fluid and at least one overexpanded internal
pressure of the balloon, whereby a resilience of the lumen wall may be
determined.
16. A body lumen cross-sectional dimension measurement catheter comprising:
a catheter body having a proximal end, a distal end, and a lumen between
the proximal end and the distal end; and
an elastomeric balloon disposed about the distal end of the catheter body,
the balloon in communication with the lumen;
a means for matching an inflated balloon cross-sectional dimension to a
body lumen cross-sectional dimension without substantially distending the
body lumen, and
a measurement element which indicates the cross-sectional dimension of the
inflated balloon.
17. A catheter as claimed in claim 16, wherein the matching means comprises
a sensor in communication with an outside surface of the catheter.
18. A catheter as claimed in claim 17, wherein the sensor comprises a
pressure sensor.
19. A catheter as claimed in claim 17, wherein the sensor comprises a flow
sensor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of medical
diagnostics, and particularly to the field of determining physiologic
characteristics of body lumens. In one particular aspect, the invention
provides methods and apparatus for measuring the cross-section of a
diseased vessel segment.
To properly treat many bodily diseases or abnormalities, certain
physiologic characteristics, such as the size of a particular body member,
often need to be determined. One example is in the treatment of vascular
lesions, stenosed regions, and particularly vascular aneurysms, which
often requires the endoluminal placement of tubular prostheses, such as
grafts, stents, and other structures. Before the prosthesis is placed in
the vascular anatomy, the size of the lesion is measured so that a
properly sized prosthesis can be selected.
Vascular aneurysms are defined as the abnormal dilation of a blood vessel,
usually resulting from disease and/or genetic predisposition which can
weaken the arterial wall and allow it to expand. While aneurysms can occur
in any blood vessel, most occur in the aorta and peripheral arteries, with
the majority of aortic aneurysms occurring in the abdominal aorta, usually
beginning below the renal arteries and often extending distally into one
or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures
where the diseased vessel segment is by-passed and repaired with an
artificial vascular graft. Recently, methods for endovascular graft
placement for the treatment of aneurysms have been proposed. One such
method and apparatus for endovascular placement of intraluminal
prostheses, including both grafts and stents, is described in co-pending
U.S. patent application Ser. No. 08/290,021, filed Aug. 12, 1994, the
disclosure of which is herein incorporated by reference. A suitable
intraluminal prosthesis for such a method includes a radially
compressible, tubular frame having a proximal end, a distal end, and an
axial lumen therebetween. The prosthesis is delivered to the area of
interest via a delivery catheter. The prosthesis is then partially
released from the catheter into a blood vessel or other body lumen to
allow the prosthesis to radially expand and conform to the interior
surface of the lumen being treated. The prosthesis can then be
repositioned by the catheter until it is properly placed within the
vessel. Optionally, the prosthesis may be implanted within a vessel by
expanding a malleable portion of the prosthesis with a balloon catheter.
Exemplary graft prostheses are described in co-pending U.S. patent
application Ser. No. 08/255,681, the disclosure of which is herein
incorporated by reference.
As previously described, before the endoluminal placement of an
intraluminal prosthesis, it is desirable to first determine the
appropriate size for the expanded prosthesis so that the prosthesis will
properly fit within the body lumen. For instance, in the case of vascular
aneurysms, it is often desirable to determine the diameter of the vessel
adjacent to the aneurysm so that the prosthesis will match the size of the
vessel on either side of the diseased area. In other circumstances, the
cross-sectional area or the circumference of a lumen would be helpful. For
example, where a prosthesis will conform to a vessel which has an
irregular cross-section, it is desirable that the periphery of the
implanted prosthesis match the lumen circumference to seal along the
periphery. Alternatively, the open cross-section area would be helpful in
determining whether placement of a prosthesis is an appropriate therapy
for a stenosed lumen. As a final example, it is desirable to select a
properly sized balloon catheter to firmly implant the prosthesis within
the vessel, but which will not over-expand the prosthesis and damage the
healthy vessel walls.
Current methods for measuring the open cross section near an effected body
lumen employ fluoroscopy. To determine the diameter of a vessel using
fluoroscopy, a catheter is inserted into the vessel and a contrast agent
is injected into the vessel through the catheter. The blood flow carries
the contrast agent along the vessel so that the vessel can be
radiographically imaged with a fluoroscope. The fluoroscope produces a
planar (or two dimensional) image of the vessel which can be evaluated to
determine the existence of a diseased or abnormal area within the vessel.
The nominal diameter of the diseased or abnormal area is then estimated by
measuring the diameter of the vessel in the area adjacent to the diseased
area on the radiographic image. However, such a measurement is typically
not particularly accurate since it relies on discerning an ill-defined
boundary in a single plane. Such a measurement does not take into account
that the vessel is usually not in the same plane as the resulting
fluoroscopic image. Another drawback to such procedures in determining the
diameter of a vessel is that the vessel is often irregular in cross
section, i.e., is not circular. Hence, even if the vessel were in the same
plane as the resulting fluoroscopic image of the vessel, it would still be
difficult to measure the open diameter of an irregular vessel.
Alternative prior art methods for measuring physiological characteristics
of lumens have stressed the diseased lumen being measured. To determine
lumen wall compliance and internal diameter, it has been proposed that a
balloon be inflated with relatively low pressure fluid within a lumen. By
monitoring inflation fluid volume and pressure, wall compliance of an
expanding lumen can be determined. By inflating the balloon with
sufficient internal pressure to expand the balloon so that it is
restrained by the lumen wall, lumen cross-sectional area or diameter can
also be measured. However, the balloon must be inflated with sufficient
pressure to ensure that it has contacted the lumen wall all along the
periphery to obtain an accurate measurement. Additionally, the measurement
balloon systems of the prior art have utilized generally cylindrical
balloons of non-compliant materials. Hence, the prior art methods have
stressed the target region of the diseased lumen by forcing irregular
lumens towards a cylindrical shape and by distending the diseased lumen.
Improper determination of the vessel size can result in the selection of a
prosthesis that is too small and hence cannot be properly grafted. The
endoluminal placement of an improperly sized prosthesis can present a
number of serious problems. One problem is that the prosthesis must be
removed from the body lumen and replaced with another that is properly
sized. This can often be difficult if the prosthesis has been radially
expanded while in the body lumen. To remove the expanded prosthesis, the
prosthesis must be radially compressed and then withdrawn from the body
lumen. Such a procedure increases the risk of injury to the patient as
well as unduly increasing operating time and expense.
Methods and apparatus are therefore needed for accurately measuring the
cross-section of a body lumen, and in particular the diameter,
circumference, and cross-sectional area of a vascular lesion. In one
particular aspect, it would be desirable to provide improved methods and
apparatus for the measurement of blood vessels in the region adjacent
aneurysms so that the proper size of intraluminal prostheses, such as
grafts and stents, can be accurately determined. It would be further
desirable if such methods and apparatus were simple to use and could be
used with existing fluoroscopy technology. Finally, it would be
particularly desirable if such measurements could be taken without causing
unnecessary stress to the diseased vessel.
2. Description of the Background Art
As previously described, methods and apparatus for placement and
repositioning of intraluminal prostheses are described in U.S. patent
application Ser. No. 08/290,021, the disclosure of which has previously
been incorporated by reference. Suitable graft structures for placement in
body lumens are described in U.S. patent application Ser. No. 08/255,681,
the disclosure of which has previously been incorporated herein by
reference.
U.S. Pat. No. 5,275,169 describes methods and apparatus for determining the
internal cross-sectional area and compliance of a vessel by measuring the
volume and pressure of an incompressible fluid within an inflated balloon
catheter. U.S. Pat. No. 4,651,738 describes a system for monitoring the
pressure-volume relationship during conventional angioplasty procedures.
U.S. Pat. No. 5,171,299 describes a similar apparatus which displays
balloon pressure and diameter based on internal balloon pressure during
angioplasty. U.S. Pat. No. 5,135,488 describes an angioplasty system
having a microprocessor for controlling, monitoring, displaying, and
recording balloon inflation data. The medical literature also describes
such measurements. See, for example, Abele (1980) AJR 135:901-906; Dembe
et al. (1991) J. Am. Coll. Cardiol. 18:1259-1262. The use of computer
enhanced radiographic imaging techniques for determining vascular lumen
diameter is described in Serruys et al. (1984) Am. J. Cardiol. 54:482-488;
and Nicols et al. (1984) Circulation 69:512-522.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for determining a
cross-sectional dimensions of body lumens, and particularly for
determining the cross-sectional area, circumference and diameter of target
regions within body lumens. Body lumens amenable to the methods and
apparatus of the present invention include blood vessels, the intestines,
the urethra, and the like. Although suitable for the measurement of most
body lumens, the present invention will find its greatest use in the
measurement of vascular lesions, particularly vascular aneurysms, vascular
stenoses, and the like. Advantageously, the cross-sectional dimensions of
such lesions can be used to select the proper size of intraluminal
prostheses, such as grafts and stents, the proper balloon for balloon
angioplasty procedures, and the proper therapy for that vascular lesion.
The methods of the present invention are carried out without disrupting the
cross-sectional characteristics being determined. According to the present
methods, a balloon catheter is inflated within a diseased lumen so that a
cross-section of the balloon substantially matches the cross-section of
the lumen being measured. The present methods then measure a
cross-sectional dimension of the balloon within the lumen. As used herein,
"cross-sectional dimension" includes all physical dimensions of the body
lumen which relate or correspond to the cross-sectional area, specifically
including the cross-sectional area, peripheral length (e.g.
circumference), width (e.g. diameter in circular vessels), and the like.
Advantageously, the present methods are performed without significantly
distending the diseased lumen prior to selection and application of an
appropriate therapy.
The present invention may advantageously be used with other apparatus and
methods for measurement of the length of vascular lesions, as disclosed in
copending U.S. patent application Ser. No. 08/380,735 (Attorney Docket No.
16380-16), the disclosure of which is herein incorporated by reference.
Broadly, the present method for measuring a cross-section of a lumen
comprises inserting a balloon catheter into the lumen, and aligning the
balloon with a target location of the lumen. The balloon is then inflated
so that a cross-section of the balloon is substantially the same as the
cross-section of the target location of the lumen. A cross-sectional
dimension of the inflated balloon is then measured, providing the
corresponding dimension of the target location of the lumen.
Advantageously, the methods of the present invention avoid the distending
of the lumen required for the pressure/volume monitoring methods of the
prior art. Instead, the present methods measure a lumen cross-sectional
dimension from a balloon inflated so as to have a cross-section that is
substantially the same as the lumen being measured, i.e. with minimal or
no luminal distension. As used herein, "substantially the same" is used to
mean that the balloon cross-section conforms to the lumen cross-section
without substantially altering the cross-sectional shape or any
cross-sectional dimension. Preferably, the balloon changes the measured
cross-sectional width by less than 5%, ideally by less than 2%.
Advantageously, the balloons of the present intention need not suffer
irreversible changes during use, and are therefore reusable. In many
embodiments, the present methods and structures allow measurement while
the balloon catheters are inflated within the body lumen.
In one aspect of the present lumen measurement method, the peripheral
surface of the balloon is conformed or matched to the lumen based on a
change in a flow through the lumen. The change is preferably measured by a
sensing a change in the flow as the balloon is expanded, preferably with a
sensor on the catheter. The expansion can thus be terminated when, for
example, the flow is substantially blocked by the balloon, before the
balloon has applied any significant force against the lumen wall.
In certain embodiments of the present method, a very flexible elastomeric
balloon is inflated using a low pressure fluid, expanding the balloon
until it is restrained by the lumen wall. The fluid is at sufficiently low
pressure that it will not distend the lumen wall, while the elastomeric
material allows the balloon to expand to conform with an irregular lumen
cross-section. Preferably, an external pressure sensor measures lumen
ambient physiological pressure to limit the required inflation fluid
pressure. The balloon thereby inflates so as to have substantially the
same cross-section as the body lumen, without substantially expanding or
otherwise traumatizing the body lumen.
Alternative embodiments of the present methods comprise expanding balloons
having a conical or tapered shape with low pressure inflation fluid until
a portion of the balloon having a cross-section smaller than the lumen is
fully expanded, while a portion of the balloon having a cross-section
larger than the lumen is not fully expanded. In such embodiments only a
portion of the balloon is matched or conformed to the cross-section of the
body lumen.
As described in more detail hereinbelow, there are several alternative
methods for measuring the cross-section of the inflated balloon. In
certain embodiments of the present method, a cross-sectional dimension of
the lumen is found by deflating and removing the balloon, and measuring
certain irreversible changes which were recorded during the maximum
expansion of the balloon within the lumen. For example, a balloon having a
plurality of internal segments, where each segment is attached to the
inside of the balloon wall to define a balloon diameter, will record a
lumen diameter by breaking those segments which are shorter than the
maximum inflated balloon diameter.
Alternative embodiments of the present methods determine the expanded
balloon cross-section in situ using remote electrical or mechanical
indicators. For example, a conductive coil which expands with the balloon
wall will vary in electrical characteristics in correlation with balloon
cross-section. Hence, measuring the resistance, inductance, or capacitance
of such an expanding conductive coil allows immediate calculation of the
inflated balloon circumference or diameter.
In further alternative embodiments, measurement elements are interpreted in
situ using known imaging modalities, such as fluoroscopy, radiography,
ultrasound, or the like. For example, a balloon having elastomeric marker
bands on the balloon wall are imaged while inflated to match the lumen
cross-section. Preferably, the marker bands provide a sharp image, and
increase in width in correlation with increasing balloon circumference,
allowing calculation of the lumen circumference from the marker band
width. Advantageously, such marker band widths could be accurately
measured using known intravascular ultrasound (IVUS) systems from within a
lumen of the catheter.
The lesion measurement catheters of the present invention comprise a
catheter body having proximal and distal ends, and a balloon disposed at
the distal end of the body. The present catheters will usually include
means for matching an inflated diameter of the balloon with a diameter of
a target location of a lumen, as described above. Preferably, the present
catheters also include a measurement element for measurement of the
inflated balloon.
Several alternative embodiments of the measurement element are described.
In a preferred embodiment, the balloon is elastomeric and includes an
external pressure sensor which indicates the pressure on the outer surface
of the catheter. Optionally, an internal pressure sensor measures the
pressure of an inflation fluid within the inflated balloon. The diameter
of an elastomeric balloon can be correlated from a difference in these two
pressures. Alternatively, monitoring the volume of an incompressible
inflation fluid allows calculation of the cross-sectional area of the
inflated balloon. Advantageously, the external pressure sensor can also
measure changes in the flow through the lumen to indicate when the balloon
has fully matched or conformed to the lumen cross-section, as described
above.
In certain embodiments the measurement element will comprise marker bands
to provide an indicator of the balloon's cross-section. Optionally, the
marker bands are visible using known imaging techniques, including
fluoroscopy, intravascular ultrasound (IVUS), and the like. Preferably,
the marker bands are elastomeric and increase in width as the balloon
expands, as described above. Alternatively, the marker bands are
conductors which change in electrical property as the balloon expands.
Alternative embodiments of the present measurement catheter comprise a
balloon and an electrical coil attached to the balloon wall so as to
expand the coil as the balloon inflates. Electrical properties of such a
coil will vary with balloon cross-sectional dimension.
Further alternative embodiments of the present catheter provide a
mechanical measurement of the balloon diameter or circumference.
Optionally, a linkage assembly expands to measure the internal balloon
diameter. Alternatively, an inelastic coil which expands with the balloon
will unwind with an increasing balloon circumference. Such mechanical
measurements are optionally imaged using fluoroscopy, X-ray, or
ultrasound, or alternatively are transmitted along the catheter body.
Still further embodiments of the present lesion measurement catheter
include at least one measurement element which is altered by expansion of
the balloon within the lumen. Optionally, a plurality of segments or disks
corresponding to varying balloon diameters are provided, at least one
corresponding to a diameter larger than the lumen and at least one
corresponding to a diameter smaller than the lumen. The image of the
segments or disks may change under fluoroscopy or ultrasound when a
balloon diameter exceeds a corresponding segment or disk diameter.
Alternatively, irreversibly overexpanded segments or disks may record the
maximum expanded diameter of the balloon after the catheter has been
deflated and removed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a first embodiment of a lumen
measurement catheter according to the present invention. The catheter is
shown with the balloon inflated within a body lumen.
FIG. 2 illustrates the catheter of FIG. 1 in a measuring position.
FIG. 3 illustrates a particular embodiment of the present catheter having
elastomeric marking bands.
FIG. 4 illustrates the catheter of FIG. 3 with the balloon inflated.
FIG. 5 illustrates an alternative embodiment of the present catheter having
bands which vary in resistance with balloon circumference.
FIG. 6 is an interior view of the catheter of FIG. 5 with the balloon
expanded.
FIG. 7 illustrates an embodiment of the present catheter having an
electrical coil which expands with the balloon.
FIG. 8 illustrates a mechanical linkage which is attached to opposing sides
of the inner surface of an alternative embodiment of the present catheter.
FIG. 9 illustrates an embodiment of the present lesion measurement catheter
having a flexible conduit attached to the balloon and an inelastic wire
disposed within the conduit.
FIG. 10 illustrates an embodiment of the present catheter having a
plurality of measurement elements.
FIG. 11 illustrates an embodiment of the present catheter having a tapered
balloon and a plurality of measurement elements.
FIG. 12 illustrates an embodiment of the present catheter having a
segmented balloon with rupture disks between segments.
DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT
The present invention provides methods and apparatus for determining
cross-sectional dimensions, such as the internal diameter, circumference,
or cross-sectional area, of a body lumen. The methods and apparatus will
preferably be used to measure the cross-section of vascular lesions, and
will find its greatest use in measuring the diameter of vascular aneurysms
and stenoses. The methods and apparatus can also find use in measuring
internal dimensions of other defects or abnormalities. Diameter and
peripheral lengths provided by the present invention will be particularly
useful in sizing intraluminal prostheses, such as vascular grafts or
stents, that are endovascularly placed within the vessel to treat the
aneurysm or other abnormality. Cross-sectional areas provided by the
invention can also be used to select the proper diameter for a balloon
angioplasty catheter or to size other therapeutic devices.
An important feature of the present invention is that it allows
cross-sectional dimensions to be measured regardless of the orientation of
the body lumen within the body. Usually, most body lumens curve throughout
the body thereby reducing the accuracy of measurements obtained from
conventional fluoroscopy procedures which produce planar images of the
lumen. The present invention takes into consideration both the varied
orientations of body lumens within the body and their irregular
cross-sectional shapes when determining their physiologic characteristics.
In making such determinations, the present invention can incorporate the
use of existing fluoroscopy technology as well as existing ultrasonic
imaging technology.
An advantage of the present invention is that the distending of the
abnormal or diseased body lumen, as associated with prior art lumen
diameter measurements, is avoided. Instead, a cross-section of the present
balloon catheter is matched with the lumen diameter. The balloon
cross-sectional dimension can then be determined, indirectly providing the
lumen diameter. Thus, a proper therapy can be selected based on the
existing dimensions of the lumen, before those dimensions are altered.
To provide such features and advantages, the invention in one exemplary
embodiment provides a luminal lesion measurement catheter 10 as shown in
FIG. 1. The catheter 10 includes an elongate tubular body 12 having a
proximal end 14, a distal end 16, and a lumen 18 therebetween. Preferably,
the length of tubular body 12 will be in the range from about 40 cm to
about 200 cm. A balloon 20 is disposed about tubular body 12 near distal
end 16. Balloon 20 usually comprises an elastomeric material such as
latex. In some embodiments, balloon 20 may alternatively comprise a
flexible, inelastic material such as polyurethane, PET, or the like.
Catheter 10 is seen in FIG. 1 inserted into a body lumen 22, with balloon
20 shown in an inflated configuration. Balloon 20 is expandable within
lumen 22 so that the balloon cross-section matches and conforms to the
lumen cross-section, but need not stress lumen 22 by expanding
substantially beyond that point. In this embodiment, expansion is
controlled using external sensor 24 attached to distal end 16 proximal of
balloon 20. As balloon 20 expands, occlusion of the body lumen will cause
a drop in pressure and a reduction in flow F. Sensor 24 may sense either
pressure or flow. Regardless, the expansion of balloon 20 is terminated
prior to expanding or stressing lumen 22.
Alternatively, expansion of the balloon may be stopped before the flow in
the lumen is completely blocked, thereby avoiding all stress on the lumen
wall, as well as the hazards of complete blockage of a lumen. Total lumen
cross-section are then found by a correlation between the balloon diameter
and the change in lumen flow, as measured at external sensor 24.
Similarly, bypass flow lumens (not shown) of known size extending from the
proximal end to the distal end of the balloon may alternatively be
incorporated.
The diameter of inflated balloon 20 is then measured to determine the
diameter of the lumen. The present invention provides several alternative
embodiments of balloon diameter measurement elements or means. Preferably,
balloon 20 comprises an elastomeric balloon having a known correlation
between internal pressure and diameter. An internal pressure sensor 26
provides the internal balloon pressure, and thereby allows balloon
diameter to be calculated from internal pressure. Preferably, internal
pressure data is combined with external pressure from sensor 24 to provide
the pressure difference across balloon 20. As the balloon diameter is most
accurately determined by this difference in pressure, this combination
provides a very precise indication of balloon diameter.
Optionally, monitoring the volume of an incompressible inflation fluid
introduced into catheter 10 from calibrated reservoir R allows the present
catheter system to measure both the cross-sectional area and compliance of
lumen 22. Once balloon 20 has been matched to the lumen cross-section as
described above, the cross-section of the balloon may be calculated from
the inflation volume and the inflated balloon length. Clearly, such a
calculation is most accurate where balloon 20 is constructed so as to
expand radially only, rather than in length.
Further inflation of balloon 20 from calibrated reservoir R will expand the
balloon outward against the lumen. Correlating the change in fluid volume
of the balloon with the change in pressure (as measured at internal sensor
26) will allow calculation of the lumen wall resilience. An alternative
apparatus and method for such a measurement is disclosed in U.S. Pat. No.
5,275,169.
FIG. 2 illustrates the lesion measurement catheter of FIG. 1 as used to
measure a blood vessel cross-section in the region adjacent to an
aneurism. Alternatively, the catheter might be used to measure the
diameter of the aneurism itself, or to measure the open cross-sectional
area of a stenosed region, or the like. Advantageously, the present
devices and methods allow such measurements without distending or
otherwise traumatizing such diseased lumens.
As shown in FIG. 2, catheter 10 has been inserted within an abnormal lumen
30 and aligned with a target region 32. The diameter of target region 32
might, for example, be needed to determine the size of an intraluminal
stent to be inserted within lumen 30. Balloon 20 is shown inflated,
thereby blocking a normal blood flow F. Thus the pressure and flow acting
on external sensor 24 has been altered. This information is transmitted to
the physician via wires 34. When flow F is completely blocked by balloon
20, the cross-section of balloon 20 has been matched to the cross-section
of target region 32 of lumen 30.
FIGS. 3 and 4 illustrate an embodiment of the present lesion measurement
catheter having marker bands for determining the inflated balloon
circumference. Catheter 10 has a balloon 40 which is elastomeric. Balloon
40 includes two radiopaque elastomeric marker bands 42 attached to the
surface of elastomeric balloon 40. FIG. 3 illustrates balloon 40 in a
relaxed configuration having diameter 44, while bands 42 have relaxed
width 46. Bands 42 will vary with the peripheral length of elastomeric
balloon 40, which in turn will vary with balloon diameter when the balloon
is not constrained. Generally, lesion measurement catheters according to
the present invention will have a relaxed or unexpanded outer diameter in
the range from 2 mm to 12 mm, preferably being in the range from 2 mm to 5
mm.
FIG. 4 illustrates balloon 40 in an expanded configuration, having an
expanded diameter 48. Fully expanded lesion measurement balloons will have
diameters in the range from 6 mm to 45 mm, preferably being in the range
from 12 mm to 32 mm. As shown here, the expanded balloon remains
unconstrained. Bands 42 of expanded balloon 40 have increased in diameter
with the balloon, with a corresponding change in measured width 50.
However, if the balloon was constrained during expansion by a lumen wall
having an irregular cross-section, it will be understood that measured
width 50 would vary with the balloon's circumference. Thus, a correlation
may be drawn between measured width 50, and balloon circumference.
Therefore, fluoroscopy or x-ray imaging which allows measurement of
measured width 50 will also provide the circumference of expanded balloon
40.
FIGS. 5 and 6 illustrate an embodiment of the present lesion measurement
catheter having conductor bands which vary in resistance with balloon
circumference. FIG. 5 shows catheter 10 having balloon 60 with three
elastomeric resistors 62. Resistors 62 are formed of a polymer or other
elastomer having known conductive properties. Suitable materials will
change in resistance in a predictable manner during elongation, such as
polyisoprene with carbon black dispersion or polysiloxane foam with
graphite impregnation.
FIG. 6 provides a cut-away view of the interior of balloon 60 in an
expanded configuration. Elastomeric resistors 62 each have a gap 64
defining two resistor ends. A wire 66 is attached to each end of the
resistor, and extends down the catheter body. As balloon 60 expands within
the lumen, elastomeric resistors 62 predictably increase in length and
resistance. Measurement of the electrical resistance while balloon 60 is
expanded within the lumen allows calculation of the peripheral length of
the expanded balloon. Alternatively, the resistors may be elastomeric
segments which are attached to opposite sides of the inner balloon surface
to define a diameter. Advantageously, the multiple resistors of this
embodiment may be used to provide information on balloon cross-section in
more than one target location.
FIG. 7 illustrates an alternative embodiment of a lesion measurement system
in which balloon cross-section is measured based on changes in the
electrical properties of a coil. A balloon 70 has a coil 72 which expands
with the inflated balloon wall. Coil 72 may be elastomeric or may
alternatively be a flexible wire riding in an elastomeric conduit, as will
be described in regard to FIG. 9. Regardless, as the balloon is inflated,
the electrical properties of coil 72 will change predictably. In some
embodiments, a central wire 74 may be attached to the distal end of coil
72. The balloon circumference and diameter may be correlated from the coil
resistance, inductance, or capacitance. Once again, a pair of wires 76
allow measurement while the catheter is inflated within the lumen.
FIG. 8 illustrates a mechanical linkage for directly measuring balloon
diameter in a further alternative embodiment of the present lesion
measurement catheter. A balloon 80 contains a linkage 82 which is bonded
to two pads 84 on opposite sides of the inner surface of balloon 80,
thereby defining a diameter. Pads 84 support four equal length links 86
which are rotatably joined to form a parallelogram. A diagonal link 88
defines a diagonal of the parallelogram, and is held by a pivot at one end
while the other end slides in a sleeve 90. The length of the parallelogram
diagonal varies with balloon diameter, allowing balloon diameter to be
read from the location of sleeve 90 relative to a set of calibrated
radiopaque marking 92 on diagonal link 88. Balloon diameter could be read
by fluoroscopy, for example. Alternatively, the diagonal link might extend
down the catheter body to be read from a calibrated scale at the proximal
end of the catheter. Clearly, a wide variety of alternative mechanical
linkages could be used.
FIG. 9 illustrates a further embodiment of the present lesion measurement
catheter comprising a balloon 100 and a flexible, inelastic coil 102.
Preferably, coil 102 is disposed within an open elastic conduit 104, which
is bonded to balloon 100. As balloon 100 expands, conduit 104 increases in
length, causing coil 102 to unwind. Preferably, one end of the coil is
fixed within the conduit, allowing the peripheral length of the conduit to
be determined by the position of the free end 108. Optionally, the coil
may be formed of a material which provides a sharp image, allowing the
coil windings or end position to be monitored by fluoroscopy, radiography,
or ultrasound. Alternatively, where the distal end of the coil is fixed,
the coil may extend down the catheter to provide an indication of the
balloon circumference at the proximal end.
As can be seen in the embodiment of FIG. 9, the catheters of the present
invention may advantageously include at least one lumen extending through
the balloon. Such a lumen may provide access for a guide wire for
repositioning the balloon, or other know intravascular devices.
Preferably, such a lumen may allow introduction of an ultrasonic
intravascular probe, as is shown in copending patent application Ser. No.
08/380,735 (Attorney Docket No. 16380-16), previously incorporated by
reference. A separate inflation lumen may also be provided (not shown).
FIG. 10 illustrates a still further embodiment of the present lesion
measurement catheter, in which a balloon 110 has a plurality of
measurement elements of varying length. The measurement elements may be in
the form of segments attached to opposite sides of the balloon wall to
define a plurality of diameters. Alternately, the elements may be disks or
the like. At least one smaller segment 112 corresponds to a diameter
smaller than the diameter of the target region of a lumen 114 to be
measured, while at least one larger segment 116 is longer. As balloon 110
is inflated to match the body lumen diameter, smaller segments 112 will be
broken, while larger segments 116 remain intact. Optionally, the segments
would be of a type which would allow visualization by known visualization
modalities. Alternatively, the maximum diameter of the inflated balloon
can be determined or confirmed after the catheter is removed.
FIG. 11 illustrates a lesion measurement catheter having a conical balloon
120. A plurality of measurement elements are provided, which may be
similar to those described regarding FIG. 10, or may advantageously be
simple marker rings which provide an image under fluoroscopy or
ultrasound, optionally comprising gold or barium sulfate. Once again, at
least one smaller ring 122 and at least one larger ring 124 are provided.
Preferably, balloon 120 is inelastic, and is allowed to expand under low
pressure until restrained by a lumen 126, as described above. The smaller
rings 122 are fully expanded, while larger rings 124 are not. When
visualized, the image of smaller rings 122 are straight and crisp, while
larger segments 124 are wavy and indistinct. Advantageously, such a
balloon would not suffer irreversible changes, and would therefore be
reusable.
FIG. 12 illustrates a final embodiment of the present lesion measurement
catheter, in which a flexible segmented balloon 130 includes a plurality
of bursting disks 132 of varying sizes. Each disk sequentially bursts
under tension as the segments expand under low pressure to fill a body
lumen 134. Segments larger than the lumen do not rupture their associated
disks, as the lumen walls absorb the outward load. The lumen diameter is
thus between the largest burst disk and the smallest intact disk. The
intact disks optionally prevent the inflation fluid from flowing into the
next larger segment, allowing balloon diameter to be measured by
incremental fluid volume. Preferably, a radiopaque fluid is retained
behind the intact disks, providing a clear indication of the lumen
diameter by the number of filled segments, as seen under fluoroscopy,
radiography, or ultrasound.
Although the foregoing invention has been described in some detail by way
of illustration and example, for purposes of clarity of understanding, it
will be obvious that certain changes and modifications may be practiced
within the scope of the appended claims.
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